Laser processing method for thin film structures

Abstract

A method of processing a thin film structure comprising: providing a thin film structure comprising a stack of two or more thin film layers supported on a surface of a substrate, the stack having a depth orthogonal to the substrate surface; and forming a cut through the depth of the stack by using a direct write laser technique to scan a laser beam along a scan path covering an area of a desired cut line on a surface of the stack to ablate material of the stack along the cut line and through the depth of the stack at least to the surface of the substrate; wherein the direct write laser technique is implemented using an ultrashort pulsed laser outputting pulses with a duration of 1000 femtoseconds or less, at a wavelength in the range of 100 to 1500 nm, and delivering a fluence in the range of 50 to 100,000 mJ/cm2.

The invention claimed is: 
     
       1. A method of processing a thin film structure comprising:
 providing the thin film structure comprising a stack of two or more thin film layers supported on a surface of a substrate, the stack having a depth orthogonal to the surface of the substrate; 
 forming a cut having a cut line width through the depth of the stack by using a direct write laser technique to scan a laser beam having a laser beam diameter or a spot width along a scan path covering an area of a desired cut line on a surface of the stack to ablate a material of the stack by creating a plasma from the material along the cut line and through the depth of the stack at least to the surface of the substrate, wherein the laser beam diameter is smaller than the cut line width and the laser beam is scanned relative to the cut line width as well as along its length to remove a required width of material; 
 wherein the direct write laser technique is implemented using an ultrashort pulsed laser outputting pulses with a duration of 1000 femtoseconds or less, at a wavelength in a range of 100 to 1500 nm, and delivering a fluence in a range of 50 to 100,000 mJ/cm 2 ; 
 and further wherein the spot width of the laser beam is 0.001 to 0.1 mm and the cut line has a width of 0.015 to 2 mm; 
 the method further comprising the steps of, after forming the cut through the depth of the stack, applying a layer of dielectric material to cover the surface of the stack, as well as to cover one or more side walls and a base of the cut; and 
 subsequently slicing through a remaining thickness of the substrate at the base of the cut. 
 
     
     
       2. The method of  claim 1 , wherein said laser outputting pulses have a duration selected from:
 a. 300 femtoseconds or less; 
 b. 200 femtoseconds or less; or 
 c. 100 to 200 femtoseconds. 
 
     
     
       3. The method of  claim 1 , wherein said laser beam is scanned along the scan path at a scan speed selected from:
 a. of 1 to 10,000 mm/s; 
 b. 50 to 600 mm/s; or 
 c. 100 to 500 mm/s. 
 
     
     
       4. The method of  claim 1 , where said pulses are output from said laser at a repetition rate selected from:
 a. 0.1 to 10,000 kHz; 
 b. 1 to 1000 KHz; 
 c. 1 to 500 KHz; 
 d. 1 to 200 KHz; 
 e. 10 to 200 kHz; or 
 f. 100 to 200 KHz. 
 
     
     
       5. The method of  claim 1 , wherein said laser beam is scanned along the scan path one or more times to ablate the material of the stack. 
     
     
       6. The method of  claim 1 , wherein said laser beam is incident on the surface of the stack with the spot width selected from:
 a. 0.001 to 0.01 mm; 
 b. 0.01 to 0.1 mm; or 
 c. 0.01 to 0.02 mm. 
 
     
     
       7. The method of  claim 1 , wherein said cut line has the width selected from:
 a. 0.1 to 2 mm; or 
 b. 0.5 to 1 mm. 
 
     
     
       8. The method of  claim 1 , wherein said laser beam is incident on the surface of the stack with the spot width which is one-fiftieth or less than the width of the cut line. 
     
     
       9. The method of  claim 1 , wherein said laser beam is incident on the surface of the stack with a spot having an intensity profile that is greatest in a centre of the spot. 
     
     
       10. The method of  claim 9 , wherein said intensity profile is a Gaussian profile or a Bessel profile. 
     
     
       11. The method of  claim 1 , wherein said ablation is continued until the cut has a depth substantially level with the surface of the substrate or is continued until the cut has a depth that extends past the surface of the substrate, wherein said depth is selected from:
 a. 500 μm or less; 
 b. 200 μm or less; 
 c. 100 μm or less; 
 d. 1-100 μm; 
 e. 1-50 μm; 
 f. 1-25 μm; 
 g. 1-10 μm; or 
 h. 10 μm or less. 
 
     
     
       12. The method of  claim 1 , wherein said depth of the stack is selected from:
 a. 200 μm or less; 
 b. 50 to 200 μm; 
 c. 5 to 100 μm; 
 d. 5 to 50 μm; 
 e. 10 to 40 μm; or 
 f. 10 to 20 μm. 
 
     
     
       13. The method of  claim 1 , wherein said laser is scanned in a sinusoidal pattern. 
     
     
       14. The method of  claim 13 , wherein said sinusoidal pattern comprises a wave with a propagation that is perpendicular to the cut line width, with peak-to-peak amplitude equal or less than the cut line width. 
     
     
       15. The method of  claim 1 , wherein said cut line is shaped to divide the stack into a plurality of elements which are isolated from one another by the cut. 
     
     
       16. The method of  claim 1 , wherein said thin film layers of the stack correspond to layers of a battery comprising:
 a. a positive electrode active material; 
 b. an electrolyte material; 
 c. a negative electrode active material; and 
 d. a negative electrode current collector. 
 
     
     
       17. The method of  claim 16 , wherein:
 a. said substrate is a conductive substrate; 
 b. said positive electrode active material is LiCoO 2 ; 
 c. said electrolyte material is LIPON, lithium borosilicate, or nitrogen doped lithium borosilicate; 
 d. said negative electrode active material is amorphous Si; and 
 e. said negative electrode current collector is platinum or molybdenum. 
 
     
     
       18. A method of fabricating a thin film battery which includes using the method of  claim 1  to form a cut which isolates an element intended for the battery from a thin film structure comprising a stack of thin film battery layers.